Turbomachines are used in a variety of useful applications. Aviation, shipping, power generation, and chemical processing have all benefited from turbomachines of various designs. In regard to general terminology, the term “turbomachine” means any machine with one or more annular blade rows exchanging energy with the fluid crossing it. Examples of turbomachines are: fans, certain types of compressors, turbines, pumps and gas turbines.
Fluid materials such as water or cooled gas may be added to a turbomachine to increase the efficiency of the turbomachine. If water is added to a compressor or the compressor section of a gas turbine, such a procedure is identified as wet compression. Wet compression enables power augmentation in turbomachine systems by reducing the work required for compression of the inlet gas. This thermodynamic benefit is realized within a compressor through “latent heat intercooling”, where water (or some other appropriate liquid) added to the gas inducted into the compressor cools that gas, through evaporation, as the gas with the added liquid is being compressed. The added liquid can be conceptualized as an “evaporative liquid heat sink” in this regard. The wet compression approach thus saves an incremental amount of work (which would have been needed to compress gas not containing the added liquid). The reduction in compressor work can be used to reduce the amount of fuel required to produce the same net output of a gas turbine (thus increasing the efficiency), or to increase the incremental amount of work available for the same gross output of the gas turbine, e.g. to drive a load attached to a turbomachine such as a generator (in the case of a single shaft machine) or to increase a compressor speed to provide more mass flow (which can have value in both single shaft and dual shaft machines).
An additional incremental contribution to power augmentation may be realized in the turbine section of a gas turbine, for instance, by a small increase in mass flow provided by the added vaporized liquid. A further incremental contribution to power augmentation also appears to be provided by an increase in gas flow which has been noted to occur with a first, 10–20 gallon per minute, increment of liquid in a large land-based power gas turbine. It should be noted that wet compression reduces the firing temperature of the turbine if the amount of fuel supplied is unchanged, and the reduced firing temperature reduces the gross output of the gas turbine. However, the reduction in compressor work is greater than the reduction in gross output of the gas turbine so that the net output of the gas turbine is increased. If the amount of fuel supplied is increased in order to raise the temperature of the cooled (respective to dry gas compression) gas/evaporated liquid mixture discharged from the compressor to the firing temperature of a gas turbine for dry compression; then the value realized from the wet compression effect is greater than the value of the additional fuel needed, resulting in value added to the operation of the system as a whole.
A risk of adding liquid to a turbomachine is blade erosion due to the impact of the liquid material on the rotating and non-rotating blades. Another difficulty with wet compression (especially in large gas turbine systems) relates to localized and non-uniform cooling (due to non-uniform distribution of the added liquid) within the turbomachine, which can distort the physical components of the turbomachine system in such a way as to cause damage from thermal stresses and from rubbing of the rotor against the inner wall of the housing and associated seals.
A further significant element of risk derives from the possibility of thermal shock if (1) the turbomachine has essentially achieved thermodynamic equilibrium and (2) the liquid addition is abruptly terminated without feed-forward compensation to the energy being added to the turbomachine; the risk is derived from a potentially damaging and abrupt transient in the internal operating temperature of the turbomachine if the evaporative liquid heat sink is removed in this manner.
Hydraulic atomizers that use the pressure of the liquid to produce droplets are commonly available, but either flow too little liquid or produce droplets that are too large. Heating the liquid so that it flashes as it leaves the atomizer can decrease the droplet size, but the rate of heat added to the liquid is equivalent to a large amount of power. Air-assisted atomizers are commonly available and can produce small droplets at a high flow rate of liquid into the gas flow path of a turbomachine, but the hardware is bulky and cannot be inserted in the gas flow path of a turbomachine without significantly disturbing the flow. Therefore, atomizers are inserted in the outer casing in order to avoid disturbing the flow. But the liquid droplets tend to remain near the outer casing due to the small size and low momentum of the droplets, so the droplets are poorly distributed, and this severely limits the efficiency improvement of adding liquid to the gas flow stream of a turbomachine. Another disadvantage is that the compression of the atomizing air used in air-assisted atomizers requires a large amount of power.
What is needed is an approach and system which enable the addition of liquid to a turbomachine to be implemented in turbomachine systems and which may reduce some or all of the disadvantages discussed above.